How do I turn a web plugin into a function for eventlistner to use

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Javascript

I need to turn this script into a function to add to eventlistner to be to use as a function

The code below is the one i need to turn into a function

<script src="https://unpkg.com/@grammarly/editor-sdk?clientId=YOUR_CLIENT_ID"></script>
<grammarly-editor-plugin>
  <textarea></textarea>
</grammarly-editor-plugin>

How can I achieve this?

The code below is an example of how I need the code to look like

<script src="https://cdn.jsdelivr.net/npm/darkmode-js@1.5.7/lib/darkmode-js.min.js"></script>
<script>
  function addDarkmodeWidget() {
    new Darkmode().showWidget();
  }
  window.addEventListener('load', addDarkmodeWidget);
</script>

What I have tried:

I havent tried anything yet i need help please